1. Field of the Invention
The present invention relates to an image processing apparatus effecting color processing with tables, and a method therefor.
2. Related Background Art
There have been proposed various color conversion technologies, in the output of color information entered for example from an image input device to a color printer or the like, for converting such color information from a device-in-dependent color space into device-dependent color components specific to the color printer. The color components entered from the image input device are three components of red (R), green (G) and blue (B), while the output color components are cyan (C), magenta (M) and yellow (Y) specific to the coloring materials in the printer. If the black color cannot be represented with these three colors, the representation is made with four colors including black (K). The conventional signal flow from the RGB input signals to the CMYK output signals is shown in FIG. 25. The input color component signals may be RGB signals based on the NTSC or PAL standards, or can also be L*a*b* signals based on the uniform color space. Means 201 for logarithmic conversion and gamma correction prepared CMY complementary color components by logarithmic conversion. (The CMY components prepared in this step are represented by C0, M0, Y0 respectively.) Then means 202 effects undercolor removal (UCR) and black generation to obtain a black (K) component. Then masking means 203 effects conversion to a device-dependent color space, matching the coloring materials specific to the printer. For this conversion, there has been proposed a method of calculating the conversion coefficients, utilizing a black box model. The equations for this conversion can be, for example, linear ones utilizing a 3xc3x973 conversion matrix or non-linear ones involving higher-order terms for improving the precision.
There is also conceived a configuration including a K term in the input of the masking means, or a configuration including the UCR itself in the masking means. Output gamma correction means 204 corrects the four color components according to the characteristics of the printer. Pseudo gradation process means 205 effects a pseudo gradation process according to the number of levels generatable by the printer, and the obtained image data are transmitted to a printer engine and printed therein.
In the conventional configuration shown in FIG. 25, there has been explained conversion means employing linear or non-linear approximation, but, in recent years, there is being principally employed methods utilizing three-dimensional color correction table for more precise conversion. For example the Japanese Patent Laid-Open Application No. 63-2669 proposes a color conversion method by so-called direct mapping, utilizing a color correction table based on all the combinations. Also there have long been proposed various methods of preparing a table with quantized lattice points of a limited number, instead of preparing all the combinations, and effecting color conversion for the input value other than the lattice points by an interpolating calculation. As an simplest example, there will be explained interpolation by 8 vertices of a cube, with reference to FIG. 26, showing the method of interpolation for an input point i, based on vertices a-h of a cube, contained in the lattice points stored in the table. The table contains the conversion information f for these vertices (f(a) to f(h) for the points a-h), the value g(e) of the point e after conversion is given by:
g(e)=(1xe2x88x92x)(1xe2x88x92y)(1xe2x88x92z)f(a)+x(1xe2x88x92y)(1xe2x88x92z)f(b)+(1xe2x88x92x)(1xe2x88x92y)zf(c)+x(1xe2x88x92y)zf(d)+(1xe2x88x92x) y(1xe2x88x92z)f(e)+xy(1xe2x88x92z)f(f)+(1xe2x88x92x)yzf(g)+xyzf(h)
This method can achieve desired color conversion in easy manner with a limited table capacity, by linear approximation with lattice points constituting a cube.
Also as another conventional example, the Japanese Patent Laid-Open Application No. 7-30772 proposes a pseudo color conversion without interpolation, by a pseudo gradation process. This method utilizes two levels of pseudo gradation process, wherein a gradation level pre-conversion effects pseudo gradation process for converting into the coordinates of optimum lattice points, in order to eliminate the input values other than the lattice points of color conversion, and a gradation level post-conversion effects quantization matching the printer, again by a pseudo gradation process. This method is based on a concept that the image quality is not affected by the limitation of the number of gradation levels by the pseudo gradation process in the pre-conversion, if a rough quantization (for example binarization) is conducted in the post conversion.
However the conventional methods explained above are associated with the following drawbacks. The color conversion process is often executed in a printer driver software on the host computer, in case of the color ink jet printer, the melting thermal transfer printer or the sublimation thermal transfer printer. With the recent improvement in the resolution of the printer engine, the number of pixels to be processed has significantly increased, so that the printer driver software requires a long process time. For this reason it is strongly desired to reduce the process time as far as possible, without deteriorating the precision of the color conversion process. In the aforementioned conventional method of calculating the corrosion value between the lattice points by interpolation, the calculation of a point g(e) requires 24 multiplications and 7 additions, leading to an enormous process time.
Also the method of the Japanese Patent Laid-Open Application No. 7-30772, employing the gradation level pre-conversion for eliminating the input values other than the lattice points prior to the input of the lattice points by the pseudo gradation process, is faster than the interpolation mentioned above, but, unless a large number of quantization levels is selected after the pre-conversion, generates a pseudo contour in the stage of pre-conversion, so that the image quality remains deteriorated also in the post-conversion. A large number of quantization levels after the pre-conversion leads to a larger table capacity, thereby increasing the load on the memory in the host computer or a longer time for the address search for such large-capacity table.
Also for a printer engine of a higher resolution, there can be conceived, for reducing the number of pixels to be processed, a method of reducing the input resolution and effecting image expansion after the color conversion, or a method of effecting an expansion at the binarization for conversion into the output resolution. In the above-explained configuration, the color conversion has to be more precise, as the resolution at the color conversion becomes lower. The image quality and the speed or the table capacity are mutually contracting requirements, and there has not been known a color conversion process satisfying all these conditions.
The foregoing conventional methods are also associated with the following drawbacks. As an example, there is considered a system in which the input resolution is different from the output resolution. The output resolution of the printers is increasing year after year, but, if the input resolution is matched with such increasing output resolution, there will result various difficulties such as the load for the preparation and processing of the image information on the host computer, the load for the color conversion and the pseudo gradation process in the printer driver, and the load of transfer time of the image information from the printer driver to the printer. It is therefore conceived a configuration of entering the information with a low resolution, thereby alleviating the load of image processing, and preparing and releasing the image information of a high resolution matching the printer engine.
The color conversion is often executed in the printer driver of the host computer, in case of the color ink jet printer, the melting thermal transfer printer or the sublimation thermal transfer printer. In such case, the color conversion is preferably executed in a low resolution state, in order to reduce the execution time. The aforementioned conventional method of calculating the correction value between the lattice points by interpolation requires 24 multiplications and 7 additions for calculating a point g(e), thus requiring an extremely long process time even if conducted with a low resolution. Also the method disclosed in the Japanese Patent Laid-Open Application No. 7-30772, of effecting pre-conversion of gradation for eliminating non-lattice input values prior to the lattice point input by pseudo gradation process is faster, but the image quality becomes deteriorated in comparison with the case of processing in the same image size, since the number of pixels required in the pseudo gradation eventually increases by the expansion process after the color conversion. If these situations are explained with reference to FIG. 26, the former method obtains g(e) by calculation but the calculated g(e) may be expanded to cover plural pixels, while, in the latter method, f(a) or f(b) may be expanded to cover plural pixels.
In these methods, it is also possible to effect image expansion for example by 0-th order interpolation prior to the color conversion, but such configuration in the former method will significantly increase the process time without improvement in the image quality, and, in the latter method, will provide certain improvement in the image quality without possibility of fine control and also will result in a significant increase in the process time.
The present invention, attained in consideration of the foregoing has the following objects.
An object of the present invention is to enable satisfactory image processing at a very high speed.
The above-mentioned object can be attained, according to an embodiment of the present invention, by an image processing apparatus for effecting image processing by N-point interpolation, utilizing lattice points stored in a table corresponding to image data, comprising:
input means for entering image data; and
interpolation means for effecting an interpolation process employing, according to said image data, lattice points not exceeding N points and including a lattice point outside an interpolating space represented by N lattice points where said image data are located.
According to the present invention there is also provided an image processing apparatus for effecting image processing with a table, comprising:
storage means for storing a table composed of data of plural lattice points indicating the relationship between input and output image data;
input means for entering image data;
first selection means for selecting, based on said input image data, data of M lattice points among the lattice point data stored in said table;
second selection means for selecting, based on relative positions of said image data with respect to each of said M lattice points, the data of N lattice points (N less than M) among those of said M lattice points; and
interpolation means for effecting an interpolation based on the data of said N lattice points, thereby determining output image data corresponding to said input image data.
Another object of the present invention is to enable high-speed image processing with a high precision of approximation.
The above-mentioned object can be attained, according to the present invention, by an image processing apparatus for effecting image processing with a table, comprising:
storage means for storing a table composed of data of plural lattice points indicating the relationship between input and output image data;
input means for entering image data;
lattice point data selection means for selecting data of lattice points of a predetermined number, based on said input image data, among the data of plural lattice points stored in said table;
calculation means for newly calculating plural data, from said selected data of the plural lattice points; and
output means for selecting, among said calculated plural data, those approximating said input image data and releasing output image data corresponding to said approximate calculated data.
Still another object of the present invention is to improve the precision of interpolation process with a simple configuration.
The above-mentioned object can be attained, according to the present invention, by an image processing apparatus comprising:
input means for entering image data;
addition means for adding a dither signal to said image data; and
interpolation means for effecting N-point interpolation, utilizing a unique interpolating space based on lattice points stored in a table corresponding to the image data with said added dither signal.
According to the present invention there is also provided an image processing apparatus comprising:
addition means for entering image information of plural color components with A bits for each color and adding a dither signal to each color component of said input image information;
quantizing means for quantizing each of the color components of said input image information with the added dither signal into M bits;
a conversion table for converting each quantized point into a quantization correction value after a color processing;
approximation means for approximating the relative position of the input point, based on N-bit information (Nxe2x89xa6Axe2x88x92M) of each color component, before elimination by said quantizing means;
calculation means for calculating corrected conversion information for the input information, based on said quantization correction value released from said conversion table.
Still another object of the present invention is to enable satisfactory conversion of resolution at a high speed.
The above-mentioned object can be attained, according to the present invention, by an image processing apparatus for effecting color correction and resolution conversion on input image data, comprising:
a table containing combinations of input image data and output image data after said color correction, for plural lattice points;
color correction means for releasing output image data corresponding to said plural lattice points, based on said input image data, by referring to said table; and
setting means for setting a number of generation of each of said output image data, based on said input image data.
According to the present invention there is also provided an image processing apparatus for entering image information composed of plural color components with n gradation levels in each color component and effecting a conversion into image information of which the number of pixels is increased to (Axc3x97B) times of the plural color components, matching the color reproduction characteristics of an image output device, comprising:
quantizing means for quantizing each of the color components of the input information;
a conversion table for converting each quantization point into a correction value matching the color reproduction characteristics of the image output device;
determination means for determining the number of generated pixels of the quantization point to be generated in the (Axc3x97B) pixels, based on the information of lower bits of each color component, eliminated by said quantization means;
gradation process means for reducing the number of gradation levels of the quantization correction value, released from said conversion table, to m levels (n less than m) by a pseudo gradation process, based on the number of generated pixels determined by said determination means; and
disposition means for positioning the pixels of m gradation levels after processing, within (Axc3x97B) pixels.